The Accuracy of Noble Gas Temperatures as a Paleoclimate Proxy: A Modeling Investigation

Noble gas temperatures (NGT) are an important terrestrial temperature proxy for the last glacial maximum (LGM) because they provide a record of mean water table temperature (WTT). For NGT to accurately represent surface air temperatures (SAT), the difference between mean annual air temperature (MAAT) and WTT must be known through time. Many paleoclimate studies reference NGT without describing the potential difference between NGT and air temperature. It is likely that some of the climatic changes that have occurred since the LGM have altered the relationship between WTT and MAAT in groundwater recharge zones. In this study, the coupling of WTT and MAAT was evaluated in numerical modeling experiments that examined WTT sensitivity to changes in: 1) precipitation amount, 2) water table depth, and 3) air temperature. Moderate changes in precipitation amount and water table depth caused minor WTT-MAAT decoupling. Varying air temperature—either MAAT or annual amplitude—changed the duration of snowcover which caused seasonal decoupling of WTT from SAT. This decoupling results in an underestimation of the actual SAT change since the LGM. Therefore, caution is necessary when inferring atmospheric temperature changes since the LGM from dissolved noble gas data in regions with seasonal snowcover.